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2295 KiB

Open AccessArticle

Rapid Synthesis and Formation Mechanism of Core-Shell-Structured La-Doped SrTiO₃ with a Nb-Doped Shell

by Nam-Hee Park, Takafumi Akamatsu, Toshio Itoh, Noriya Izu and Woosuck Shin

Materials 2015, 8(7), 3992-4003; https://doi.org/10.3390/ma8073992 - 2 Jul 2015

Cited by 4 | Viewed by 5963

Abstract

To provide a convenient and practical synthesis process for metal ion doping on the surface of nanoparticles in an assembled nanostructure, core-shell-structured La-doped SrTiO₃ nanocubes with a Nb-doped surface layer were synthesized via a rapid synthesis combining a rapid sol-precipitation and hydrothermal [...] Read more.

To provide a convenient and practical synthesis process for metal ion doping on the surface of nanoparticles in an assembled nanostructure, core-shell-structured La-doped SrTiO₃ nanocubes with a Nb-doped surface layer were synthesized via a rapid synthesis combining a rapid sol-precipitation and hydrothermal process. The La-doped SrTiO₃ nanocubes were formed at room temperature by a rapid dissolution of NaOH pellets during the rapid sol-precipitation process, and the Nb-doped surface (shell) along with Nb-rich edges formed on the core nanocubes via the hydrothermal process. The formation mechanism of the core-shell-structured nanocubes and their shape evolution as a function of the Nb doping level were investigated. The synthesized core-shell-structured nanocubes could be arranged face-to-face on a SiO₂/Si substrate by a slow evaporation process, and this nanostructured 10 μm thick thin film showed a smooth surface. Full article

(This article belongs to the Special Issue Low-Dimensional Anisotropic Thermoelectrics)

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1077 KiB

Open AccessArticle

Synthesis and Thermoelectric Properties in the 2D Ti_{1 – x}Nb_xS₃ Trichalcogenides

by Patrick R. N. Misse, David Berthebaud, Oleg I. Lebedev, Antoine Maignan and Emmanuel Guilmeau

Materials 2015, 8(5), 2514-2522; https://doi.org/10.3390/ma8052514 - 11 May 2015

Cited by 25 | Viewed by 7056

Abstract

A solid solution of Ti_{1 − x}Nb_xS₃ composition (x = 0, 0.05, 0.07, 0.10) was synthesized by solid-liquid-vapor reaction followed by spark plasma sintering. The obtained compounds crystallize in the monoclinic ZrSe₃ structure type. For the [...] Read more.

A solid solution of Ti_{1 − x}Nb_xS₃ composition (x = 0, 0.05, 0.07, 0.10) was synthesized by solid-liquid-vapor reaction followed by spark plasma sintering. The obtained compounds crystallize in the monoclinic ZrSe₃ structure type. For the x = 0.07 sample, a mixture of both A and B variants of the MX₃ structure is evidenced by transmission electron microscopy. This result contrasts with those of pristine TiS₃, prepared within the same conditions, which crystallizes as a large majority of A variant. Thermoelectric properties were investigated in the temperature range 323 to 523 K. A decrease in the electrical resistivity and absolute value of the Seebeck coefficient is observed when increasing x due to electron doping. The lattice component of the thermal conductivity is effectively reduced by the Nb for Ti substitution through a mass fluctuation effect and/or a disorder effect created by the mixture of both A and B variants. Due to the low carrier concentration and the semiconductor character of the doped compounds, the too low power factor values leads to ZT values that remain smaller by a factor of 50 than those of the TiS₂ layered compound. Full article

(This article belongs to the Special Issue Low-Dimensional Anisotropic Thermoelectrics)

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1148 KiB

Open AccessCommunication

Enhanced Thermoelectric Performance of Bi₂O₂Se with Ag Addition

by Bin Zhan, Yaochun Liu, Jinle Lan, Chengcheng Zeng, Yuan-Hua Lin and Ce-Wen Nan

Materials 2015, 8(4), 1568-1576; https://doi.org/10.3390/ma8041568 - 1 Apr 2015

Cited by 46 | Viewed by 6890

Abstract

Polycrystalline Bi₂O₂Se/Ag nanocomposites were synthesized by spark plasma sintering process. Their thermoelectric properties were evaluated from 300 to 673 K. With the addition of silver, the conductive second phase Ag₂Se and Ag can be observed, which results [...] Read more.

Polycrystalline Bi₂O₂Se/Ag nanocomposites were synthesized by spark plasma sintering process. Their thermoelectric properties were evaluated from 300 to 673 K. With the addition of silver, the conductive second phase Ag₂Se and Ag can be observed, which results in a significant enhancement of electrical conductivity. The maximum conductivity is 691.8 S cm⁻¹ for Bi₂O₂Se/20 vol.% Ag, which increased nearly 500 higher times than the pure Bi₂O₂Se bulk. ZT value can be enhanced greatly, ~0.07, for Bi₂O₂Se/5 vol.% Ag at 673 K, which is two times larger than the pure sample. Full article

(This article belongs to the Special Issue Low-Dimensional Anisotropic Thermoelectrics)

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625 KiB

Open AccessArticle

Structure and Transport Properties of the BiCuSeO-BiCuSO Solid Solution

by David Berardan, Jing Li, Emilie Amzallag, Sunanda Mitra, Jiehe Sui, Wei Cai and Nita Dragoe

Materials 2015, 8(3), 1043-1058; https://doi.org/10.3390/ma8031043 - 12 Mar 2015

Cited by 32 | Viewed by 9115

Abstract

In this paper, we report on the crystal structure and the electrical and thermal transport properties of the BiCuSe_1−xS_xO series. From the evolution of the structural parameters with the substitution rate, we can confidently conclude that a complete solid [...] Read more.

In this paper, we report on the crystal structure and the electrical and thermal transport properties of the BiCuSe_1−xS_xO series. From the evolution of the structural parameters with the substitution rate, we can confidently conclude that a complete solid solution exists between the BiCuSeO and BiCuSO end members, without any miscibility gap. However, the decrease of the stability of the materials when increasing the sulfur fraction, with a simultaneous volatilization, makes it difficult to obtain S-rich samples in a single phase. The band gap of the materials linearly increases between 0.8 eV for BiCuSeO and 1.1 eV in BiCuSO, and the covalent character of the Cu-Ch (Ch = chalcogen element, namely S or Se here) bond slightly decreases when increasing the sulfur fraction. The thermal conductivity of the end members is nearly the same, but a significant decrease is observed for the samples belonging to the solid solution, which can be explained by point defect scattering due to atomic mass and radii fluctuations between Se and S. When increasing the sulfur fraction, the electrical resistivity of the samples strongly increases, which could be linked to an evolution of the energy of formation of copper vacancies, which act as acceptor dopants in these materials. Full article

(This article belongs to the Special Issue Low-Dimensional Anisotropic Thermoelectrics)

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761 KiB

Open AccessArticle

Fe-Doping Effect on Thermoelectric Properties of p-Type Bi_0.48Sb_1.52Te₃

by Hyeona Mun, Kyu Hyoung Lee, Suk Jun Kim, Jong-Young Kim, Jeong Hoon Lee, Jae-Hong Lim, Hee Jung Park, Jong Wook Roh and Sung Wng Kim

Materials 2015, 8(3), 959-965; https://doi.org/10.3390/ma8030959 - 5 Mar 2015

Cited by 25 | Viewed by 7474

Abstract

The substitutional doping approach has been shown to be an effective strategy to improve ZT of Bi₂Te₃-based thermoelectric raw materials. We herein report the Fe-doping effects on electronic and thermal transport properties of polycrystalline bulks of p-type Bi [...] Read more.

The substitutional doping approach has been shown to be an effective strategy to improve ZT of Bi₂Te₃-based thermoelectric raw materials. We herein report the Fe-doping effects on electronic and thermal transport properties of polycrystalline bulks of p-type Bi_0.48Sb_1.52Te₃. After a small amount of Fe-doping on Bi/Sb-sites, the power factor could be enhanced due to the optimization of carrier concentration. Additionally, lattice thermal conductivity was reduced by the intensified point-defect phonon scattering originating from the mass difference between the host atoms (Bi/Sb) and dopants (Fe). An enhanced ZT of 1.09 at 300 K was obtained in 1.0 at% Fe-doped Bi_0.48Sb_1.52Te₃ by these synergetic effects. Full article

(This article belongs to the Special Issue Low-Dimensional Anisotropic Thermoelectrics)

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Review

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4023 KiB

Open AccessReview

Misfit Layer Compounds and Ferecrystals: Model Systems for Thermoelectric Nanocomposites

by Devin R. Merrill, Daniel B. Moore, Sage R. Bauers, Matthias Falmbigl and David C. Johnson

Materials 2015, 8(4), 2000-2029; https://doi.org/10.3390/ma8042000 - 22 Apr 2015

Cited by 58 | Viewed by 10887

Abstract

A basic summary of thermoelectric principles is presented in a historical context, following the evolution of the field from initial discovery to modern day high-zT materials. A specific focus is placed on nanocomposite materials as a means to solve the challenges presented by [...] Read more.

A basic summary of thermoelectric principles is presented in a historical context, following the evolution of the field from initial discovery to modern day high-zT materials. A specific focus is placed on nanocomposite materials as a means to solve the challenges presented by the contradictory material requirements necessary for efficient thermal energy harvest. Misfit layer compounds are highlighted as an example of a highly ordered anisotropic nanocomposite system. Their layered structure provides the opportunity to use multiple constituents for improved thermoelectric performance, through both enhanced phonon scattering at interfaces and through electronic interactions between the constituents. Recently, a class of metastable, turbostratically-disordered misfit layer compounds has been synthesized using a kinetically controlled approach with low reaction temperatures. The kinetically stabilized structures can be prepared with a variety of constituent ratios and layering schemes, providing an avenue to systematically understand structure-function relationships not possible in the thermodynamic compounds. We summarize the work that has been done to date on these materials. The observed turbostratic disorder has been shown to result in extremely low cross plane thermal conductivity and in plane thermal conductivities that are also very small, suggesting the structural motif could be attractive as thermoelectric materials if the power factor could be improved. The first 10 compounds in the [(PbSe)1+δ]m(TiSe2)n family (m, n ≤ 3) are reported as a case study. As n increases, the magnitude of the Seebeck coefficient is significantly increased without a simultaneous decrease in the in-plane electrical conductivity, resulting in an improved thermoelectric power factor. Full article

(This article belongs to the Special Issue Low-Dimensional Anisotropic Thermoelectrics)

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5448 KiB

Open AccessReview

Chemical Potential Tuning and Enhancement of Thermoelectric Properties in Indium Selenides

by Jong-Soo Rhyee and Jin Hee Kim

Materials 2015, 8(3), 1283-1324; https://doi.org/10.3390/ma8031283 - 20 Mar 2015

Cited by 29 | Viewed by 8944

Abstract

Researchers have long been searching for the materials to enhance thermoelectric performance in terms of nano scale approach in order to realize phonon-glass-electron-crystal and quantum confinement effects. Peierls distortion can be a pathway to enhance thermoelectric figure-of-merit ZT by employing natural nano-wire-like electronic [...] Read more.

Researchers have long been searching for the materials to enhance thermoelectric performance in terms of nano scale approach in order to realize phonon-glass-electron-crystal and quantum confinement effects. Peierls distortion can be a pathway to enhance thermoelectric figure-of-merit ZT by employing natural nano-wire-like electronic and thermal transport. The phonon-softening known as Kohn anomaly, and Peierls lattice distortion decrease phonon energy and increase phonon scattering, respectively, and, as a result, they lower thermal conductivity. The quasi-one-dimensional electrical transport from anisotropic band structure ensures high Seebeck coefficient in Indium Selenide. The routes for high ZT materials development of In₄Se₃₋_δ are discussed from quasi-one-dimensional property and electronic band structure calculation to materials synthesis, crystal growth, and their thermoelectric properties investigations. The thermoelectric properties of In₄Se₃₋_δ can be enhanced by electron doping, as suggested from the Boltzmann transport calculation. Regarding the enhancement of chemical potential, the chlorine doped In₄Se₃₋_δCl_0.03 compound exhibits high ZT over a wide temperature range and shows state-of-the-art thermoelectric performance of ZT = 1.53 at 450 °C as an n-type material. It was proven that multiple elements doping can enhance chemical potential further. Here, we discuss the recent progress on the enhancement of thermoelectric properties in Indium Selenides by increasing chemical potential. Full article

(This article belongs to the Special Issue Low-Dimensional Anisotropic Thermoelectrics)

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3337 KiB

Open AccessReview

Hierarchical Architecturing for Layered Thermoelectric Sulfides and Chalcogenides

by Priyanka Jood and Michihiro Ohta

Materials 2015, 8(3), 1124-1149; https://doi.org/10.3390/ma8031124 - 16 Mar 2015

Cited by 66 | Viewed by 11275 | Correction

Abstract

Sulfides are promising candidates for environment-friendly and cost-effective thermoelectric materials. In this article, we review the recent progress in all-length-scale hierarchical architecturing for sulfides and chalcogenides, highlighting the key strategies used to enhance their thermoelectric performance. We primarily focus on TiS₂-based [...] Read more.

Sulfides are promising candidates for environment-friendly and cost-effective thermoelectric materials. In this article, we review the recent progress in all-length-scale hierarchical architecturing for sulfides and chalcogenides, highlighting the key strategies used to enhance their thermoelectric performance. We primarily focus on TiS₂-based layered sulfides, misfit layered sulfides, homologous chalcogenides, accordion-like layered Sn chalcogenides, and thermoelectric minerals. CS₂ sulfurization is an appropriate method for preparing sulfide thermoelectric materials. At the atomic scale, the intercalation of guest atoms/layers into host crystal layers, crystal-structural evolution enabled by the homologous series, and low-energy atomic vibration effectively scatter phonons, resulting in a reduced lattice thermal conductivity. At the nanoscale, stacking faults further reduce the lattice thermal conductivity. At the microscale, the highly oriented microtexture allows high carrier mobility in the in-plane direction, leading to a high thermoelectric power factor. Full article

(This article belongs to the Special Issue Low-Dimensional Anisotropic Thermoelectrics)

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2314 KiB

Open AccessReview

Recent Progress on PEDOT-Based Thermoelectric Materials

by Qingshuo Wei, Masakazu Mukaida, Kazuhiro Kirihara, Yasuhisa Naitoh and Takao Ishida

Materials 2015, 8(2), 732-750; https://doi.org/10.3390/ma8020732 - 16 Feb 2015

Cited by 199 | Viewed by 16814

Abstract

The thermoelectric properties of poly(3,4-ethylenedioxythiophene) (PEDOT)-based materials have attracted attention recently because of their remarkable electrical conductivity, power factor, and figure of merit. In this review, we summarize recent efforts toward improving the thermoelectric properties of PEDOT-based materials. We also discuss thermoelectric measurement [...] Read more.

The thermoelectric properties of poly(3,4-ethylenedioxythiophene) (PEDOT)-based materials have attracted attention recently because of their remarkable electrical conductivity, power factor, and figure of merit. In this review, we summarize recent efforts toward improving the thermoelectric properties of PEDOT-based materials. We also discuss thermoelectric measurement techniques and several unsolved problems with the PEDOT system such as the effect of water absorption from the air and the anisotropic thermoelectric properties. In the last part, we describe our work on improving the power output of thermoelectric modules by using PEDOT, and we outline the potential applications of polymer thermoelectric generators. Full article

(This article belongs to the Special Issue Low-Dimensional Anisotropic Thermoelectrics)

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